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Imagine eating that same bowl of warm, fluffy rice you had for lunch, but only absorbing half of its calories. It may sound like a dieter’s dream, but scientists are close to making it reality, simply by changing the way rice is cooked.

This method, developed by scientists at the Institute of Chemistry’s College of Chemical Sciences in Sri Lanka, decreased the 240 calories in a cup of rice – they used a Sri Lankan variety known as Bg 305 – by 10 to 15 per cent.

If the best rice variety, such as Suduru Samba – a short-grain rice grown in Sri Lanka and parts of India – is used, the method could reduce calories by 50 to 60 per cent compared to a cup cooked in the normal way, lead scientist Sudhair A. James told the South China Morning Post.

James explained that starch can be digestible or indigestible. Rice is loaded with both types, though some varieties naturally contain more indigestible – or what the scientists call “rice resistant” – starch, which contributes extremely few calories compared to digestible starch.

“Because obesity is a growing health problem, especially in many developing countries, we wanted to find food-based solutions,” said James. “We discovered that increasing rice-resistant starch concentrations was a novel way to approach the problem.”

In Hong Kong, where rice is a staple, this finding could potentially help reduce obesity rates.

Because obesity is a growing health problem, especially in many developing countries, we wanted to find food-based solutions

Sudhair A. James

Unlike digestible types of starch, rice-resistant starch is not broken down in the small intestine, where carbohydrates normally are metabolised into glucose and other simple sugars, and absorbed into the blood stream.

“Moreover, rice-resistant starch is fermented in the large intestine by the gut microflora and converted to short-chain fatty acids and other by-products,” said James. “These in turn confer well-being [on] the host by aiding in lipid oxidation, colon conditioning, and many other benefits as well.”

Thus, the researchers set out to transform digestible starch into rice-resistant starch. They experimented with 38 kinds of Sri Lankan rice varieties.

According to their analysis, Bg 305 had the lowest natural concentration of rice-resistant starch. The top three varieties in terms of rice-resistant-starch concentration were Suduru Samba, Thatuwee and Bg 3-5.

Through trial and error, they developed the cooking method, which increased concentrations of rice-resistant starch in the Bg 305 rice by a factor of 10.

How can such a simple change in cooking result in a lower-calorie food? James explained that the oil enters the starch granules during cooking, changing its architecture so that it becomes resistant to the action of digestive enzymes. This means that fewer calories ultimately get absorbed into the body.

"The cooling is essential because amylose, the soluble part of the starch, leaves the granules during gelatinisation,” explained James. “Cooling for 12 hours will lead to formation of hydrogen bonds between the amylose molecules outside the rice grains, which also turns it into a resistant starch."

Reheating the rice for consumption, he noted, did not affect the levels of rice-resistant starch.

Is the rice cooked through this method still delicious, though?

“After the primary sensory evaluation, the taste was the same and it was delicious,” said James. However, he noted “a slight difference” to the rice texture and said his team was working to improve this, with results ready in two to three months’ time.

As for the feasibility of going through such a relatively tedious rice cooking process instead of the typical half-hour or so the traditional method takes, James recommended cooking the rice in 2 to 3 kilogram batches and storing it in the fridge till needed.

James will present his study findings at this week’s 249th National Meeting & Exposition of the American Chemical Society in the American city of Denver.

He added: “However, we are working on another alternative method and instead of cooling the rice for 12 hours, we are trying to freeze it.”

James made clear that rice is not inherently bad for health. When taken in the right amount – according to age and body mass – it serves the required nutrients to any healthy individual, he said.

"After your body converts carbohydrates into glucose, any leftover fuel gets converted into a polysaccharide carbohydrate called glycogen," he explained.

"Your liver and muscles store glycogen for energy and quickly turn it back into glucose as needed. The issue is that the excess glucose that doesn't get converted to glycogen ends up turning into fat, which can lead to excessive weight or obesity."